A Penn State study found that young boys adjusted how much they ate at a meal when they had already consumed a fruit snack, while girls did not. The researchers interpret this as an indication that boys in this age group more reliably respond to internal hunger and fullness signals, whereas girls may be more influenced by social or environmental cues when determining portion size and intake.
The study also tested whether the form of the fruit—slices, purée, or juice—changed overall food intake. After controlling visual cues and eating pace, the research team found no meaningful difference in total calories consumed based on the apple form for the group as a whole. The sex differences in compensation for the preload, however, were notable.
Key findings
- Boys’ response: Boys reduced calories at the meal after a fruit snack, showing near-perfect compensation.
- Girls’ response: Girls ate about the same amount at the meal regardless of a prior fruit snack.
- Food form: Apple slices, applesauce, and apple juice had similar effects on overall satiety when visual and pacing cues were controlled.
- Implication: Early sex differences in eating regulation may reflect socialization and could influence long-term eating habits.
Source: Penn State
Study design and procedures
The study included 64 children (32 boys and 32 girls) aged four to six years. Each child visited the laboratory five times, with about a week between sessions, and experienced five conditions in randomized order: no preload (control) or one of four equal-calorie apple preloads—slices, purée, juice, or a lower-calorie sweetened juice. Visual cues about portion size were masked by using a container shaped like an apple, and researchers controlled eating rate by reading an apple-themed story that cued children to take each snack portion at specified times.
Approximately eight minutes after the snack and the story, the children were offered an ad libitum meal that included macaroni and cheese, carrots, grapes, graham crackers, broccoli and water. Researchers weighed remaining food to calculate exact intake. Children who refused the meal due to picky eating were excluded from the final analysis.
Results: food form and sex differences
When the researchers pooled all children together, food form did not significantly alter total energy intake. Overall calorie compensation across conditions showed that children adjusted their meal intake to account for the preload. However, when the sample was examined by sex, a clear difference emerged: boys adjusted their meal calories to nearly fully compensate for the snack, while girls did not adjust their meal intake in the same way.
Specifically, boys showed near-perfect compensation for apple slices, indicating they reduced meal calories by an amount close to the snack energy. Girls’ compensation tended to exceed or remain unchanged relative to the preload, suggesting other factors guided their meal intake beyond immediate physiological satiety cues.
Possible explanations for sex-based differences
The experiment did not measure the exact mechanisms behind these sex differences, but the lead researcher, Kathleen Keller, points to two plausible contributors. First, socialization and cultural messaging about food and body size differ for males and females and may begin early in life. Girls often receive stronger messages about appearance and eating behaviors, and they typically show greater social compliance, which could make them more responsive to external cues—how much others eat, adult prompts, or perceived expectations—rather than internal hunger signals.
Second, developmental differences in the pace of social maturation may play a role. Infants of both sexes initially regulate intake based on internal cues, but as children grow they learn social signals about eating. Prior research indicates girls develop social responsiveness earlier than boys, which may explain why girls in this age range were less guided by satiety cues and more by learned behaviors or environmental signals.
Practical implications: relearning internal cues
Keller emphasizes that attention to social cues has clear benefits—children learn what foods are safe and acceptable by observing caregivers and peers—but in environments with abundant high-calorie foods, overreliance on external cues can contribute to overeating, weight gain, or disordered eating patterns. Re-encouraging children to notice internal signals of hunger and fullness may help promote healthier eating habits.
For parents and caregivers, the researchers recommend encouraging children to pay attention to how they feel internally when deciding whether to eat. Although schedules and routines often require structured mealtimes, helping children distinguish between eating for hunger and eating for other reasons—boredom, habit, or social prompts—can build better self-regulation around food.
Study authors, funding and publication
The study was led by Kathleen Keller and included contributions from Barbara Rolls, Benjamin Baney, Lori Francis, Kristin Buss, Tracy Winfree, John Hayes, Nicole Reigh, Marion M. Hetherington, Kameron Moding, Samantha MR Kling and others. Funding was provided by the Penn State Social Science Research Institute. The full open-access paper is titled “Effects of apple form on satiety in 4–6 year-old children: possible evidence of sex differences” and appears in the journal Appetite.
Abstract (summary)
Research in adults shows food form (liquid, semi-solid, solid) can influence satiety even when energy and energy density are matched, but less is known about children. In a crossover study with 64 children (mean age 5.9 years), preloads of apple slices, purée, and juice (matched for energy) or no preload were presented with visual cues masked and eating rate controlled. Children then ate ad libitum from a standardized meal. Overall, food form did not significantly influence satiety, but results varied by sex: boys showed near-perfect compensation for preloads while girls did not, suggesting satiety in girls may be more influenced by social or learned cues and satiety in boys by biological signals.
Author: Christine Yu; Source: Penn State; Image credited to: Neuroscience News